THE FEEDING VALUE OF TOWER RAPESEED FOR EARLY-WEANED PIGS. I. EFFECTS OF METHODS OF PROCESSING AND OF DIETARY LEVELS

Abstract

Tower rapeseed (Brassica napus L.), either autoclaved (121 °C, 103 kPa, 30 min), dry-heated (130 °C, 1 h) or extruded (85 °C, 30 sec), was fed to early-weaned pigs in wheat-based diets also containing pea protein concentrate. In the first three experiments, 20 or 24% rapeseed (RS) was included in the diets; in the fourth experiment, 10 and 20% levels of RS were fed. Extrusion and dry heating were only partially effective but autoclaving completely inactivated myrosinase, and reduced isothiocyanate content and the availability of lysine. Thyroid histology and function reflected the goitrogenicity associated with residual myrosinase activity in the processed RS. Increasing the dietary levels of autoclaved RS from zero to 20% of the diet had no effect (P < 0.05) on growth, feed intake, efficiency of utilization of dietary energy and protein or on thyroid or liver weights. Digestibility coefficients for dry matter, protein, energy and crude fibre were reduced at the 20% level of RS. However, hyperplasia and hypertrophy of follicular epithelium were found in thyroids of pigs fed 10 and 20% RS. Thyroxine and protein-bound iodine values tended to decrease, and blood cholesterol and thiocyanate values to increase, with increasing levels of dietary RS. Liver and kidney sections were normal. No glucosinolates were detected in the gastrointestinal tract but urinary thiocyanate excretion increased with the level of RS fed.